1. Field of the Invention
This invention relates to lithium-germanium containing electrodes for electrical energy storage batteries, batteries containing such negative electrodes and a process for fabrication of such electrodes from materials in the charged and uncharged state.
2. Description of the Prior Art
Utilization of liquid lithium for the negative electrode of a lithium-metal sulfide battery has been proposed due to its low equivalent weight and high cell voltage, thereby providing the potential for higher battery energy densities. The liquid lithium has been retained in a foraminous metal substrate by capillary action for use as a negative electrode. However, under operating conditions of a secondary battery containing a molten salt electrolyte, the electrolyte has been found to react with the lithium and after operation of such a battery for a number of cycles, the liquid lithium leaves the metal substrate increasing cell component corrosion and problems of containment of liquid lithium causing cell instability. Attempts to overcome such problems have been suggested by U.S. Pat. Nos. 3,409,465 and 3,634,144.
The use of solid lithium alloys, such as lithium-aluminum and lithium-silicon, has been suggested as a negative electrode in secondary molten salt batteries. The lithium-aluminum alloy discharges at a cell potential approximately 300 millivolts more positive than liquid lithium, has a capacity of 0.8 Ahr/g and has shown good electrochemical reversability. However, the lithium-aluminum alloy electrode suffers large changes in volume during charging and discharging of the cell and upon cell cycling the alloy morphology changes resulting in loss of capacity. U.S. Pat. No. 3,506,490 suggests alloys such as lithium-aluminum to form a solid electrode material and U.S. Pat. Nos. 3,506,492 and 3,508,967 relate to solid lithium anodes.
The lithium-silicon alloy electrode structure has been suggested by U.S. Pat. No. 3,969,139. However, the lithium-silicon electrode has a capacity of 2.12 Ahr/g and has shown acceptable electrochemical reversability, but when utilized at high current densities the lithium-silicon alloy electrodes tend to become polarized during electrochemical transfer of lithium and it has been observed that silicon migrates from the active electrode portion into the ferrous current collector resulting in embrittlement of the current collector leading to breakdown of the electrode structure. U.S. Pat. No. 4,048,395 teaches lithium-silicon-iron alloys for use as negative electrodes to overcome the tendency of the electrode to polarize at high current densities. The lithium-silicon-iron alloy, however, did not cure the silicon migration into the metal supporting structure causing embrittlement. U.S. Pat. No. 4,076,905 teaches a lithium-silicon-boron alloy for use as a ternary alloy electrode. While the incorporation of boron into the alloy reduces silicon migration, the embrittlement problem has not been completely solved.